Fuel for spark ignition internal combustion engines



FUEL FOR SPARK IGNITION INTERNAL COMBUSTION ENGINES Euphime V. Bereslavsky, New York, N. Y., assignor to Sinclair Refining Company, New York, N. Y., a corporation of Maine No Drawing. Application May 31, 1955, Serial No. 512,325

7 Claims. (CI. 44-69) This invention is an improved liquid fuel of the gasoline type and additive therefor, for an internal combustion engine of the higher compression ratio range employing an electric spark for igniting the combustible fuel mixture, and an improved method of operating such an engine.

According to the invention, the fuel is a blend of a conventional hydrocarbon motor fuel of appropriate boiling range and octane number, tetraethyl lead in the usual range of amounts, and a smaller amount of one or more compounds selected from the trialkyl phosphines, as described more fully below, with or without other additives.

The trialkyl phosphines are a known but little used group of compounds. Their preparation is well enough known to need no description here. The general empirical formula is RsP, in which R is an alkyl group which need not be the same at all three positions in the molecule. The trialkyl phosphines which are useful for the present purpose are those in which the alkyl groups are in the range from methyl (CH3) to amyl (CsHn) inclusive, namely, C1 to C3 alkyl groups, primary and secondary C4 alkyl groups, and primary C5 alkyl groups. Of these useful compounds, the preferred species are those in which at least two of the alkyl groups are in the range from C2 to C4. inclusive, but excluding (as indicated) the tertiary C4 isomer, the third alkyl group being in the range from C1 to C5. This preferred group thus includes, in addition to the compounds having the same alkyl group at all three positions, such compounds as diethyl methyl phosphine, diethyl propyl phosphine, diethyl isopropyl phosphine, the diethyl butyl phosphines, and the diethyl amyl phosphines.

The predominant component or" the fuel blend is the hydrocarbon material which is a mixture of hydrocarbons boiling in the gasoline range from an initial of about 120 F. to a 90% point of about 400 F. or somewhat lower, and an end-point of about 440 F., all as measured by the A. S. T. M. distillation method. In the case of an aviation fuel, the 90% point and the end-point are lower, but within the range stated. The octane range, in terms of Research octane number, is upwards of 85, and includes the range above 100 now identified primarily with fuel for aircraft spark-ignition engines and rated in terms of performance number. The octane value, in addition to being increased by the tetraethyl lead additive, may be the result of special catalytic or pyrolytic conversion processing or of other additives such as alkylates or other hydrocarbons having a very high octane blending number. I refer to this major component of theblend as high octane gasoline.

The above described trialkyl phosphines are present in my blend in an amount which, by volume, ranges from about 0.2 cc. per gallon to about 1 cc. per gallon of hydrocarbon fuel. More than 1 cc./gal. can be used, but the excess is not economically justified in most cases. Essentially the same values represent also the proportion of the phosphine in the total blend. In percentage terms, the range is from about 0.005% to about 0.025%, by volume, of the blend. Within the stated range, smaller amounts of the lower alkyls, e. g., Cg, are needed than of 2,797153? Patented June 25, 1951 the higher alkyls. For the preferred examples, 0.3 cc. of triethyl phosphine correspond in effect to about 0.4 cc. of tripropyl phosphine and to about 0.5 cc. of tributyl phosphine.

The engines in which the invention has its utility are those spark-ignition internal combustion engines in which the compression ratio is above 7.5 :1, recognized as the range of higher compression engines. The best results are obtained with engines having a compression ratio in the range of about 8.5 :1 and above. In present practice, the ratio ranges up to 10:1, and in the future it may go to 12:1.

The utility of the invention is that such an engine, when supplied with the described fuel in admixture with air for combustion, suffers fewer deposit-induced or surface ignitions and produces less spark plug fouling than when operated with the same fuel without the trialkyl phosphine. The engine thus delivers more power, because of the reduced loss from abnormal combustion. Compared with known fuel blends having additives to attain this same objective, my fuel requires a smaller weight of additive to achieve an acceptable reduction of abnormal combustion and, further, by causing thinner deposits in the combustion space, it minimizes the increase in the octane requirement of the engine caused by the deposits.

A number of compounds of phosphorous have been tested in the past as fuel additives with widely variant results. So far as I know, this work has been largely if not wholly empirical, leading to no reliable theory of ac tion by which useful compounds can be selected or by which all of the dilferences in results can be explained. On this empirical basis, and despite controversy concernmg its net value, tricresyl phosphate (TCP) has come to be regarded by many as a desirable phosphorous compound; and in any event has gained extensive commercial use. In general, the amount of tricresyl phosphate additive is about 0.67 cc./ gal. at most for a gasoline containmg 3 cc./ gal. of tetraethyl lead. Even this amount causes certain disadvantages, so that larger amounts are avoided and smaller amounts are sometimes used. The other phosphorous compound which has gained commercial acceptance is chloropropyl thionophosphate, usually called IQC. This is used in substantially the same amount, or slightly smaller amount, around 0.55 cc./gal. (0.70 gm./ gal.) with generally comparable results.

Comparative tests have shown that my fuel is able to match and in some respects to improve upon the performance of an otherwise identical fuel containing tricresyl phosphate, and that this result is possible with an amount of trialkyl phosphine (TAP) in my fuel equal to little more than half by Weight of the amount of tricresyl phosphate (TCP) in the comparison fuel. These tests were made using the single cylinder test procedure in which deposits are accumulated for a period of 40 hours under cyclic conditions representative of different operating conditions of a motor car. The total number of deposit-induced ignitions were detected by means of an ionization gap and were counted automatically. The base fuel was composed of catalytically cracked stock and 10% of motor alkylate, with 3.0 ml. of tetraethyl lead, and was representative of commercial premium gasoline for automobile use. The crank-case lubricant was an all distillate Mid-Continent base stock. Five comparative fuels were run, as follows:

A--Base fuel (control) as above.

B-Base fuel plus 0.51 cc./ gal. of tri-n-butyl phosphine. C-Base fuel plus 0.67 cc./ gal. of tricresyl phosphate. DBase fuel plus 1.00 cc./ gal. of tri-n-butyl phosphine. EBase fuel plus 1.34 cc./ gal. of tricresyl phosphate.

The count of the number of deposit-induced ignitions We... a

for 40 hours showed the following results (namesof additives being abbreviated):

1 The test showing this valueinvolved excessive oil consumption, so

that this value is abnormallyhigh by some unknown amount. h Having regard to the limits of -statistical significance of such test data, it is believed to be a conservative evaluation of these result to say (1) that both my fuel and the TCP fuel gave very materially less abnormal combustion than the-control fuel; (2) that my fuel with 0.51 cc./gal. of TAP is equal to --a fuel with 0.67 cc. gal. of TCP, which is the maximum amount of TCP customarily used, this amount being based'on theso-called 0.2 Theory basis for the 3 ml. of TEL;(3) that an increase of the content of TAP in my fuel gave no significant difference in result; and (4) that while doubling the content of TCP to 1.34 cc./,gal, gave some improvement, the result in a practical view was not enough better to justify the increased cost of the additive and the increase in deleterious effects which it would involve.

Thus my fuel is as effective in this respect as a commercial motor fuel having tricresyl phosphate, and it achieves the commercially acceptable degree of improvement with a materially smaller amount of additive. The volume ratio of 0.51 to 0.67 as given above corresponds to a weight ratio of 0.414.gm./gal. to 0.7926 gm./gal. .of fuel blend; and from the practical standpoint, since such materials are purchased by weight, the significant fact is that little more than half the weight of tributyl phosphine is needed to match the effect of the maximum commercially used quantity of tricresyl phosphate.

In the particular comparative tests reported above, made by an independent group, no measurements were reported in other respects, but on the basis of observation it was reported that as far as could be determined the fuel with the trialkylphosphine was equivalent to the fuel with tricresyl phosphate in respect of distribution of the additive within the combustion chamber, build- -up of deposit on the valves, spark plug fouling and gasoline stability. Other tests have shown that visual observation fails to reveal significant differences in the amount of deposits, so that the conclusion as to equivalence in this respect has to be taken in the light of the results of measurements of the total deposit in other tests.

In another set of tests by another independent group, employing similarly a single cylinder CFR test engine procedure but a different method of counting the number of surface or deposit induced ignitions in a 40 hours period, the base fuel used as a control was a commercial premium grade gasoline having 3 cc./ gal. of TEL and a Research octane number of 92. It showed a count ,of 135. The same fuel with an addition of 0.55 cc./gal. (0.70 gm./gal.) of the additive known as ICC (chloropropyl thionophosphate) showed a count of 53, which is a distinct improvement with respect to abnormal combustion and an improvement representative of what is commercially acceptable, warranting use of the additive.

My fuel, tested in comparison with these, consisted of a commercial premium gasoline of 95 octane number -(Research) having 3 cc./gal. of TEL and 0.5 cc./gal. of tri-n-butyl phosphine. This same fuel without that addition of the phosphine was generally comparable with the base fuel of the ICC test, although somewhat higher in "octane number (95 vs. 92'), and is referred to below as the second base fuel of this series of tests. It showed a count of 140, which is typical of commercial premium gasolines having no additive to reduce abnormal combustion. In contrast, my fuel showed-a-count of only 47, as an average of four runs, evidencing a superior performance in reduction of abnormal combustion,

Equally significant in this series of tests were the observations and measurements of total deposits within the combustion space. The first base fuel (92 octane) showed small total deposits (not measured but estimated at about 5 to 6 grams in total). The same gasoline with the ICC additive produced more deposit, the average total deposit being 10.5 .grams. Atnoted above,'the fuel with this additive nevertheless reduced the'abnormal combustion attributed to deposits. The total deposit produced with the second base fuel (95 octane) was measured, and averaged 5.3 grams. My fuel, consisting of this second base fuel with 0.5 cc./ gal. of tri-n-butyl phosphine, produced a total deposit which averaged only 6.5 grams, little if any more than that produced by the base fuel alone and markedly less 'than 'the deposit of 10.5 grams with the ICC fuel. Yet my fuel reduced abnormal combustion, as above, by somewhat more than did the ICC fuel; i. e'., in terms of the count, from 140 to 47 in the case of my fuel as compared with a reduction from to 53 in the case of the ICC fuel.

The practical significance of the smaller deposit produced'with my fuel is that there'is less increase of the octane requirement of the engine. One of the chief disadvantages attending the use of'known additives to lessen .abnormalcombustion is that they increase the amount of deposit within the combustion space and thereby materially reduce-the volume of'that space. This effect takes on greater importance in the case of the higher compression ratio engines in which the combustion space is smaller. Ineffect, these additives increase the compression ratio of the engine. A fuel having the octane num- 'ber appropriate to the designed compression ratio is therefore unable to give the same anti-knock performance 'after the formation of such extensive deposits. To obtain the intended anti-knock performance requires a fuel of higher octane number; and this effect has become so well known as to acquire a name, the octane requirement increase or URL Some have even questioned whether the advantage of the known commercial additives such as TCP and ICC in reducing the abnormal combustion caused by deposits is not off-set by the adverse effect upon the octane requirement of the engine, since an increase of even one point in octane number of a motor fuel involves a very large cost.

My fuel, while capable of achieving the commercially acceptable degree of reduction of abnormal combustion, does so with a smaller increase in total deposit and therefore with a lesser increase in octane requirement; and it does this with little more than half the weight of additive. It is believed that prolonged use of my fuel will also show the deposit to be of a less adherent nature, more readily removable, and that this characteristic of the deposit may be related to its effect of leaving a thinner deposit in that the engine purges itself of a greater part of the depositing or deposited material. It is amply clear on the evidence already at hand that the chemical composition of the deposit formed with my fuel is different from that produced with fuels containing phosphates, and that the complex'chemical action of the trialkyl phosphines in conjunction with the tetraethyl lead, the hydrocarbons and the products of'combustion is critically different from the action of fuels containing phosphates.

Further advantages of the described trialkyl phosphines "are that they are readily miscible 'with tetraethyl lead fluid, that they are more soluble in hydrocarbon fuels than TCP and ICC, and that as a class they are more compatible with gasolines in specific gravity and boiling point. Thus, a single additive composed of tetraethyl lead and the trialkyl phosphine can be prepared, in inti- .mate mixture, with .or without a solvent carrier; and better distribution throughout the gasoline can thereby be obtained than when thephosphine is added alone.

In specific gravity, thetrialkyl phosphinesrange from about 0.8 to 0.815, where TCP and ICC have specific gravities above 1.1 and therefore markedly different from the gravity of the gasoline component of the fuel, which ranges around 0.7. The greater compatibility of the trialkyl phosphines in this respect promotes the maintenance of good distribution of the additive throughout the gasoline.

The preferred trialkyl phosphines, in which the alkyl groups are in the range from C2 to C4, have boiling points which either lie in or lie close to the boiling range of automotive gasoline. The C4 species, tri-n-butyl phosphine, has the highest boiling point of the preferred class, around 465 R, which is slightly above the usual gasoline end-point. Nevertheless, in admixture with the gasoline, this substance presents no significant difference from the heavier gasoline fractions in volatility characteristic because of the familiar partial pressure effect. Even the methyl species, boiling separately at little over 100 F. and therefore in the range of the lightest gasoline fractions, creates no incompatibility in volatility characteristic when mixed with the gasoline.

I am aware of the prior proposal that the trialkyl phosphines generally, and Without discrimination among the different species, be used as an additive to diesel fuels for compression ignition engines. See Nygaard et 211., U. S. P. No. 2,368,866. The stated purpose and result were to shorten the ignition delay period of such engines or, in other Words, to accelerate the ignition of the fuel when compressed. To that end, the amount of trialkyl phosphine used was from 0.1% to 5.0%, and preferably from about 0.25% to about 2.0%. I distinguish my concept from that in these several respects, namely, that I deal with a different base fuel (gasoline instead of diesel fuel) and a different type of engine (spark ignition); that my fuel includes tetraethyl lead; that I employ an amount of phosphine of a different order of magnitude, and employ a more restricted group of the trialkyl phosphines; and that my result as to ignition is not an acceleration but a retardation, in that (inter alia) my fuel reduces preignition by so-called surface or deposit-induced ignitions ahead of the desired spark ignition.

Iclaim:

1. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together with tetraethyl lead and from .005 to .025 by volume of at least one trialkyl phosphine selected from the class of such phosphines in which the alkyl groups are selected from the group consisting of C1 to C3 alkyl groups,

primary and secondary C4 alkyl groups and primary C5 alkyl groups.

2. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together with tetraethyl lead and from .005% to .025 by volume of at least one trialkyl phosphine selected from the class of such phosphines in which the alkyl groups are selected from the group consisting of C1 to C3 alkyl groups, primary and secondary C4 alkyl groups and primary C5 alkyl groups, with the proviso that at least two of the alkyl groups are selected from the group consisting of C2 to C3 alkyl groups and primary and secondary C4 alkyl groups.

3. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together with tetraethyl lead and from about 0.2 cc./gal. to about 0.5 cc./gal. of at least one trialkyl phosphine selected from the class of such phosphines in which the alkyl groups are selected from the group consisting of C1 to C3 alkyl groups, primary and secondary C4 alkyl groups and primary C5 alkyl groups.

4. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together with tetraethyl lead and from about 0.2 cc./gal. to about 0.5 cc./gal. of at least one trialkyl phosphine selected from the class of such phosphines in which the alkyl groups are selected from the group consisting of C1 to C alkyl groups, primary and secondary C4 alkyl groups and primary C5 alkyl groups, with the proviso that at least two of the alkyl groups are selected from the group consisting of C2 and C3 alkyl groups and primary and secondary C4 alkyl groups.

5. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together with about 3 cc./gal. of tetraethyl lead and about 0.3 cc./ gal. of triethyl phosphine.

6. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together with about 3 cc./ga1. of tetraethyl lead and about 0.4 cc./gal. of tripropyl phosphine.

7. A fuel for higher compression internal combustion engines employing spark ignition which comprises high octane gasoline as a predominant component together With about 3 cc./gal. of tetraethyl lead and about 0.5 cc./gal. of tributyl phosphine.

References Cited in the file of this patent UNITED STATES PATENTS 1,575,440 Midgley Mar. 2, 1926 2,265,819 Rosen Dec. 9, 1941 2,405,560 Campbell Aug. 13, 1946 FOREIGN PATENTS 1,043,087 France Nov. 5, 1953 695,841 Great Britain Aug. 19, 1953 709,471 Great Britain May 26, 1954 

1.A FUEL HIGHER COMPRESSION INTERNAL COMBUSTION ENGINES EMPLOYING SPARK IGNITION WHICH COMPRISES HIGH OCTANE GASOLINE AS A PREDOMINANT COMPONENT TOGETHER WITH TETRAETHYL LEAD AND FROM .005% BY VOLUME OF AT LEAST ONE TRIALKYL PHOSPHINE SELECTED FROM THE CLASS OF SUCH PHOSPHINES IN WHICH THE ALKYL GROUPS ARE SELECTED FROM THE GROUP CONSISTING OF C1 TO C3 ALKYL GROUPS, PRIMARY AND SECONDARY C4 ALKYL GROUPSS AND PRIMARY C5 ALKYL GROUPS. 